Plastics are used for many automobile decorative parts and are often electroplated (e.g., with chromium) to achieve a particular aesthetic effect. Decorative chromium plating customarily comprises successive electrodeposited layers of copper, nickel and chromium as is well known in the art. The electrodeposit must adhere well to the underlying plastic substrate even in corrosive and thermal cycling environments, such as are encountered in outdoor service and environment testing. In order to obtain durable and adherent metal deposits, the substrate's surface must be conditioned or pretreated to insure that the electrodeposits adequately bond thereto.
For strength and cost reasons, mineral-filled nylon is a very desirable plastic for many automobile applications. The term "mineral-filled nylon" (hereinafter MF-nylon) as used herein refers to plating grade polyamide resins which contain powdered (i.e., 0.2-20 microns) mineral fillers such as talc, calcium silicate, silica, calcium carbonate, alumina, titanium oxide, ferrite, and mixed silicates (e.g., bentonite or pumice). Such MF-nylons are commercially available from a variety of sources having mineral contents of up to about forty percent by weight and include such commercial products as Capron CPN 1030 (Allied Chemical), Nylon 540-110-HSP (Firestone), Minlon 11C-40 (DuPont) and Vydyne R-220 or RP 260 (Monsanto). Heretofore, a variety of wet processes have been proposed to condition or pretreat MF-nylon for electroplating. Such wet pretreatment processes call for immersion of the parts in a series of chemical solutions ending in the electroless deposition of a thin adherent metal blanket on the part which serves to conduct the electroplating current and anchor the electrodeposit to the part. Generally speaking, these wet processes have included etching the MF-nylon in such solutions as chromic-sulfuric acid, trichloroacetic acid, formic acid, sulfuric-hydrochloric acid, or iodine-potassium iodide solutions; catalyzing the surface to promote the electroless deposition; and finally the electroless deposition of Cu or Ni on the surface. Unfortunately, MF-nylon is hygroscopic and hence absorbs large quantities of water during such processing which must be removed (e.g., by baking or "normalizing" at elevated temperatures) in order to insure long term durability of the plated part. This, coupled with the environmental, safety, controllability and excessive processing time considerations associated with processing parts through a series of solutions, makes the wet processes quite costly. Proprietary pretreatment processes are commercially available from such companies as the MacDermid and the Shipley Companies among others.